Note sur le genreChoricystis (Chlorophyceae)

This paper deals with the systematic position ofChoricystis. Its species and their synonyms are studied. Five species are considered to belong to the genera. The study has mainly been based on the original diagnosis and iconotypes. The author has also studied some samples ofCh. chodatii taken from damp soils of Argentina.     

Remarques sur la matrice des chondrites ordinaires d'apres l'observation de quelques chondrites a bronzite peu ou pas choquees

Microscopic investigations have been done on the chondrites Sena and Nadiabondi (H5, not shocked), Ste. Marguerite en Comines (H4, very slightly shocked), Allegan (H5, slightly shocked). Only in such cases can the matrix be easily observed and compared to those of type 3 chondrites. The <100 μm debris found in types 4 and 5 that we have observed are not the result of the metamorphism of type 3 fines.The abundance of tiny debris is in direct relation with the intensity of the shock though this shock was insufficient to provoke either the induration of the stones or a significant loss of rare gases. The bulk of the fines are the result of local disaggregation of the most brittle parts from chondrules and fragments.A low-temperature matrix has not been observed in these meteorites but only in H3 chondrites, as a coating around the chondrules. The accretion modelists should take into account the absence or the scarcity of fine particles in their calculations.     

Premières données sur l'évolution quantitative des entomostracés planctoniques dans le lac Léman

The increasing eutrophication of lake Geneva (lake Léman) induced a more than twofold increase of the mean annual zooplankton biovolume from 1959 to 1982.      

Investigations Nouvelles sur les Gaz Volcaniques

The analyses which have so far been made of volcanic gases have only given instantaneous measurements of the composition of the gas phase which, however, is likely to be variable during periods of eruptive activity. A first step towards the continuous measurement of fluctuations in the composition of the gas phase during eruptions was made in 1963, by the use of sampling tubes permitting the rapid determination in the field of individual components of gaseous emanations. Since then, a technique has been developed of collecting samples of volatile constituents and preserving them for subsequent analyses in the laboratory. On the other hand, a technique has been developed for continuous sampling with a distant recording mechanism, which permits the study of the dynamics of eruptive phenomena. The first results of observations on several different types of emanations (submarine, high and low temperature fumaroles, and gas discharges from basalt flows) may considered satisfactory. The present paper is intended to encourage volcanologists concerned with the study of eruptive phenomena to employ new methodes for the study of this problem. The analysis of the eruptive mechanisms should start with a simultaneous observation and recording of the greatest possible number of parameters. The gas phase is of fundamental importance in the eruptive phenomena. It is therefore indispensable to understand its variations with time, both rapid and slow. It is very important to be able to show, on the same diagram, curves representing the simultaneous variations of all the measurable parameters, chemical, physical, and mechanical.     

In Memoriam: David le Sueur

Biography

In Memoriam: David le Sueur     

Note sur la famille des Oscillatoriacées

Owing to a critical examination of the taxonomic characteristics ofOscillatoria, such as gas vacuoles, calyptra, sheath, arrangement of the trichome, etc., this family has to be redefined. It is divided into two tribes:

1. The ‘Vaginariées’ or rather the Schizothricées (Oscillatoria which have developed sheaths withseveral trichomes).
2. The ‘Lyngbyées’, with or without sheath which only contain one trichome.

The first tribe includes the speciesSchizothrix (encompassingHydrocoleum, Dasygloe, Oligoclonium, Lyngbyopsis), Microcoleus (withSirocoleus) andPorphyrosiphon. The tribe of the ‘Lyngbyées’ is composed of theOscillatoria species (includingSpirulina, Arthrospira, Spirulinopsis, Glaucospira [?] andJuguspira [?]),Lyngbya (withPhormidium, Symploca, Katagnymene, Pelagothrix, Haliarachne, Proterendothrix, Cirrosiphon, Cyanohydnum) andCrinalium. The systematic position fo the four speciesIsocystis, Borzia, Sinaiella andPseudanabaena is somewhat doubtful and must be examined more closely for clarification.     

Visual characterization technique for gravel‐cobble river bed surface sediments; validation and environmental applications Contribution to the programme of CIRSA (Centre Interuniversitaire de Recherche sur le Saumon Atlantique)

This paper presents an evaluation of the feasibility and the reliability of a visual characterization technique for gravel–cobble river bed surface substrate. Based on principal axis regressions, using phi scale (ϕ), comparisons of visual estimation and grid sampling techniques show that useful predictive relations (R² = 0·78–0·88) exist between visual estimates of the surface d₁₆, d₅₀ and d₈₄ and estimates obtained for the same percentiles with the grid sampling technique. Comparisons of visual estimation and the surface‐bulk sampling technique also indicate a predictive relation (R² = 0·70) between the d₅₀ of the two methods. Trained operators can visually estimate gravel–cobble bed surface d₁₆ to uncertainties of 41 per cent, d₅₀ to 15 per cent and d₈₄ to 11 per cent (for example, there is a 5·5 mm error on a d₈₄ size of 50 mm). Furthermore, evidence shows that if operators are properly trained, a calibration relation for each percentile can be applied independently of operators. This visual characterization allows effective detailed mapping of spatial patterns in substrate size distribution along extensive reaches of gravel‐bed rivers. The technique can be very useful in creating terrain models for various geomorphological, hydrological and biological applications such as the determination of entrainment thresholds, hydraulic roughness and substrate suitability for benthic insects or salmonid habitat. Copyright © 2001 John Wiley & Sons, Ltd.     

Sur le developpement de la Glaciologie Suisse

Sans résumé     

Un modèle de prévision géologique sur la base des observations de la prospection magnétique — application de la théorie de la corrélation multiple

Résumé On fait une application particulière de la théorie de la corrélation et de la régression pour l'interprétation des données résultant d'une prospection magnétique. Est déterminée, en premier lieu, la corrélation multiple entre l'intensité de la composante verticale du champ magnétique, la teneur en Fe et la profondeur d'un complexe porteur de minéralisations de fer. Le seconde partie de l'ouvrage présente un modèle d'estimation du contenu de fer et du volume de complexe minéralisé sur la base des courbes de régression déterminées. Dans la troisième partie du travail est effectué un calcul des erreurs d'appréciation de la qualité et de la quantité des réserves.     

Simulation d'une pollution sur un champ captant aupres d'un fleuve—suivi dans l'espace et dans le temps a partir d'un traceur NaCl á l'aide d'une méthode électrique

The aim of the technique described here is to follow displacement of a NaCl trace (brine), simulating pollution, in extent and time, from a river towards water boreholes in operation. 30–50 V electrodes, monitored simultaneously through passage of a direct current, provide the position of the NaCl “cloud” and in what time period it has appeared at each electrode in relation to the initial ground conditions prior to introducing the brine. Preferred seepage paths, foci of pollution flow, are thus exposed. The sequence of readings has been specially formulated with this objective in mind.A full-scale example of the application is presented (River Ain, France).     

Les courbes flux chimique-debit et le fonctionnement des aquiferes karstiques

When integrating both chemical content and discharge, the chemical flux is a choice parameter, as much for the study of water transit as for weathering budgets.

In a karst system, the flux allows the identification of: (a) the main aquifer of the system that supplies the spring to the point of complete drying-up; (b) the “piston-effect” of seepage upon highly mineralized waters contained in karst channels; (c) the qualitative passage from a regime of water decline to one of water depletion; (d) several outlets belonging (or not) to the same karst system; (e) the homogeneity in the capability of mixing the system, and thus, a contrario, the importance of its karstification; (f) the heterogeneity of seepage and of reserves.

Abstract

Intégrant à la fois la concentration chimique et le débit qui la véhicule, le flux chimique est un paramètre de choix autant pour l'étude des transits d'eau que pour celle des bilans de l'altération.

Dans le système karstique, le flux permet d'identifier: (a) l'aquifère principal du système, capable d'alimenter la source jusqu'au tarissement total; (b) le phénomène d' “effet-piston” de l'infiltration sur les eaux minéralisées présentes dans les drains; (c) le passage qualitatif de la décrue au tarissement au cours d'une récession; (d) l'appartenance ou non de plusieurs exutoires au même système karstique; (e) l'homogénétité et les qualités de bon mélangeur du système et donc, à contrario, l'importance de sak arstification; (f) l'hétérogénéité de l'infiltration ou celle des réserves.     

Mises au point sur les différents facteurs physico-chimiques influant sur la mesure de concentration de traceurs fluorescents et leurs conséquences pratiques en hydrologie

The use of xanthenic dyes in hydrology can, in certain circumstances, lead to alteration in the quantitative interpretation of the experimental results due to failure to recognize the physico-chemical phenomena which affect the measurement of fluorescence, namely, the nature of the solvent, pH, temperature and the presence of mineral salts.In this paper we recall the essentials of these mechanisms and illustrate the consequences. In succession, some particular circumstances of the use of fluorescent xanthenic tracers (in environments with strong ionic activity, in the presence of sodium iodide, and in the presence of deactivating saline ions) are examined as well as the precautions which users must observe to maintain the quality of the measurements and to prevent photodegradation or absorption processes.Attention is drawn to the difficulties of interpreting the measurements of concentration of the fluorescent-tracer elutant collected on activated carbon (“fluotransducers”) and a method of measurement, by selective extinction, is proposed for two fluorescent tracers present simultaneously in the same environment.